Thank you for the DLC, Ellendyl! But unfortunately there seems to be a problem with Humble Bundle. Could you please open a support ticket there and send your transaction ID? Sorry for the inconvenience.

Below is the reply I got from Humble Bundle support:

Thank you for reaching out to Humble Bundle Support. I'm sorry to hear about the trouble you've been having with that gift!
Before we can look into this for you, we'll need to verify the order details with the original purchaser due to privacy concerns. Would you mind having the person who sent the gift submit a ticket with the Transaction ID (a 13-digit code that begins with X) for their order? Once we have that, we can verify the purchase and look into the matter further.
Once they open a ticket, simply reply here with that ticket number and I'll reach out to your friend to resolve the issue.
Please let me know if you have any other questions in the meantime. All the best,
-Zoe
Humble Bundle
http://support.humblebundle.com/

Support ticket #1593633